A technique with which a terminal unit having a communicating means performs playback and reception of multimedia data in parallel, is called streaming play or simply streaming. Streaming enables a terminal to reproduce long multimedia data having a greater amount of data than the memory capacity of the terminal, and enables multimedia data to start playing without waiting for the entire data to download.
As typical streaming protocols, RTP (Real-Time Transport Protocol) and RTCP (RTP Control Protocol) (RFC1889) for data transmission, RTSP (Real-Time Streaming Protocol) (RFC2326) for session control can be mentioned, and they are used for exchange of data and control information between the transmitting side (server) and receiver and player side (terminals) in a system (streaming system) that handles streaming.
The server in a streaming system needs to continue supplying multimedia data at a proper transmission rate to the terminal side so as not to cause receiver buffer overflow or underflow of the multimedia data to be played on the terminal, or so that congestion will be unlikely to occur on the network en route. Since the transmission rate required by multimedia data occupying the transmission band is generally large, in most of the conventional streaming systems, the communicating means is continuously used during a session (e.g., a sequence of data communication from the beginning to the end of a certain unit of transmission data) (this will hereinbelow be referred to as “1st prior art”).
For portable type wireless communication terminals which mostly have a lower amount of memory capacity, streaming is effective in playing long content. However, since wireless communication is the most power consumptive process, portable type wireless communication terminals, which are in most cases driven by batteries, have suffered from the rapid battery exhaustion problem with the conventional streaming system that continuously uses the communicating means during play.
On the other hand, there have been some technologies of reducing power consumption of wireless communicating means without missing any transmitted data by using intermittent communication, though they are not aimed at application to streaming. Examples of such technologies include the power saving mode defined in the ARIB (Association of Radio Industries and Business) standard T70 (commonly called “HiSWANa”), the power saving mode defined in IEEE standard 802.11 and the technology disclosed in Japanese Patent Application Laid-open Hei 7-67164.
In any of the technologies, the transmitting side wireless appliance repeatedly transmits data within every limited period while the receiving side receives the transmitted data by keeping synchronization with the transmitting side by an appropriate means. In this operation, since data transmission stops in the time span from the end of transmission of a certain period to the beginning of the next period, it is stated that power consumption can be cut down by shutting the electric supply to the communicating means of the receiving side wireless appliance during the time span (this will hereinbelow be referred to as “2nd prior art”).
However, since the above second prior art judges that operation should be switched to the intermittent communication mode if the state where the amount of communication per unit time between the wireless communication terminal and the base station is low has persisted for a certain period of time, this method has not been applied to the streaming systems that use the communicating means continuously through the entire session.
If intermittent communication is simply applied to a streaming system, there occurs the problem of data underflow (a lack of data) on the receiving side during a halt of data transmission since, once power supply to the communicating means is stopped, data cannot be received from the cessation to the start of the next intermittent period.
As the countermeasure against occurrence of underflow, it is possible to consider a system in which transmission of multimedia data starts first so that the data can be buffered previously before streaming playback starts. However, in portable wireless communication terminals, which mostly have a low memory capacity, there occurs the problem in that the requirement for reception buffer memory capacity cannot be met if too much buffering is done.
The present invention has been devised in order to solve the above problems, it is therefore an object of the present invention to provide a data communication apparatus and its intermittent communication method, which can cut down the power consumption in the wireless communication process during streaming while the requirement for reception buffer memory capacity can be met when streaming playback is performed in a wireless communication terminal.